use std::collections::HashSet;

struct Test {
    data_hash_set: HashSet<String>,
    test_hash_set: HashSet<String>,
}

impl Test {
    fn new() -> Test {
        Test {
            data_hash_set: HashSet::new(),
            test_hash_set: HashSet::new(),
        }
    }
}

fn main() {
    let mut test = Test::new();

    test.data_hash_set.retain(|item| !test.test_hash_set.contains(item));
}